Ferrite body containing metallization

ABSTRACT

A composite comprised of a sintered matrix of spinel ferrite and a non-exposed continuous phase of elemental silver or Ag-Pd alloy ranging to 25 atomic % Pd is produced by co-firing a laminated structure of ferrite powder-containing tapes containing non-exposed metallization-forming material. The composite can be formed into a composite product which contains a continuous silver or Ag-Pd alloy phase with two end portions wherein only the end portions are exposed.

Copending U.S. patent application for "Ferrite Composite ContainingSilver Metallization", Ser. No. 172,834 filed on Mar. 25, 1988, now U.S.Pat. No. 4,880,599 in the names or R. J. Charles and A. R. Gaddipati,assigned to the assignee hereof and incorporated herein by reference,discloses the production of a composite comprised of a sintered matrixof spinel ferrite and an electrically conductive phase of elementalsilver by co-firing a laminated structure of ferrite powder-containingtapes containing a silver metallization-forming material having two endportions wherein only the end portions are exposed.

This invention relates to the production of a sintered compositecomprised of a sintered ceramic ferrite matrix containing a continuousmetal phase, i.e. metallization, of elemental silver, or of a Ag-Pdalloy which ranges in Pd content to 25 atomic %, wherein the metal phaseis not exposed to the ambient. The composite is useful for producing acomposite product containing an electrically conductive metallization ofsilver, or of the Ag-Pd alloy, with two end portions wherein only theend portions are exposed to the ambient.

The low melting point (961° C.) and high vapor pressures of silver atthe temperatures required for the co-firing of silver metallized spinelferrites limit the practical use of silver as a metallization to itsalloys with other precious metals. In particular, due to requisitemelting points, metal/ceramic adhesion requirements and cost, the mostcommon alloys utilized are those with palladium wherein palladiumcontents generally exceed 30 atomic %. A very large penalty results fromthe use of even 70/30 Ag-Pd since the resistivity of this alloy at 20°.C is of the order of 20 times that of silver.

The present invention enables the formation of a continuousmetallization of silver in a co-fired ferrite body.

In another embodiment, the present invention enables the formation of acontinuous metallization of an alloy of silver and palladium in theco-fired ferrite body. The present Ag-Pd alloy ranges in Pd content toabout 25 atomic % and it is molten or partially molten at the maximumfiring temperature, i.e. sintering temperature. By partially molten itis meant herein that at least about 5% by volume of the Ag-Pd alloy ismolten. Generally, the Pd content of the alloy ranges from a detectableamount, i.e. an amount detectable by microprobe analysis, to about 25atomic %, frequently from about 1 atomic % to about 20 atomic %, or fromabout 2 atomic % to about 10 atomic %. An alloy comprised of about 75atomic % Ag-25 atomic % Pd has a solidus (fully solid) temperature ofabout 1100° C. and a liquidus (fully molten) temperature of about 1190°C. As the Pd content of the alloy decreases, its solidus and liquidustemperatures decrease. The use of the present Ag-Pd alloy may makeprocessing easier.

Briefly stated, the present process for producing a solid sinteredcomposite comprised of a sintered ferrite matrix totally enveloping acontinuous metallization of elemental silver, or of a Ag-Pd alloyranging in Pd content to 25 atomic %, said ferrite matrix having aresistivity greater than 500 ohm-centimeters, comprises:

(a) providing a ferrite powder;

(b) admixing said ferrite powder with an organic binding material;

(c) forming the resulting mixture into tape;

(d) providing a silver or Ag™Pd alloy metallization-forming material;

(e) forming a layered structure of at least two of said tapes containingsaid metallization-forming material therewithin in a pattern, saidmetallization-forming material being present in an amount sufficient toproduce said metallization;

(f) laminating the layered structure forming a laminated structurewherein none of said pattern is exposed;

(g) firing said laminated structure to thermally decompose its organiccomponent at an elevated temperature below about 600° C. leaving nosignificant deleterious residue in the resulting fired structure, saidfiring being carried out in an atmosphere or vacuum which has nosignificant deleterious effect on said composite;

(h) sintering the resulting fired structure at a temperature rangingfrom about 1000° C. to about 1400° C. in an oxygen-containing atmosphereto produce a sintered product having the composition of said composite,at least about 5% by volume of said Ag-Pd alloy being molten at saidsintering temperature, said fired structure having a sufficient openvolume available to accommodate the silver or Ag-Pd alloy duringsintering; and

(i) cooling said sintered product to produce said composite, saidsintering and cooling being carried out in an atmosphere which has nosignificant deleterious effect on said composite; said ferrite powderhaving a composition which forms said ferrite matrix in said process.

In carrying out the present process, a ferrite powder is provided whichproduces the present sintered ferrite matrix having an electricalresistivity greater than 500 ohm-centimeters, preferably greater than100,000 ohm-centimeters, at a temperature ranging from about 20° C. toabout 100° C. These powders are available commercially or can beprepared by standard ceramic processing, generally by calcining aparticulate mixture of the constituent oxides which react by solid-statediffusion to form the desired ferrite which is then milled to producethe desired particle size distribution. By "resistivity" herein, it ismeant the electrical resistance of the present sintered ferrite in theform of a bar one centimeter long and one square centimeter incross-section.

The ferrite powder is a magnetic oxide. The term "magnetic" is usedherein to indicate a material which is magnetized by a magnetic field.The ferrite powder is known in the art as a spinel ferrite and it is ofcubic symmetry. The present ferrite powder has a composition representedby the formula MO(Fe₂ O₃)₁±x where x has a value ranging from 0 to about0.2, preferably ranging from 0 to about 0.1, and where M is a divalentmetal cation selected from the group consisting of Mg, Mn, Fe, Co, Ni,Zn, Cu, and a combination thereof. Representative of useful ferritesinclude nickel zinc ferrite and manganese zinc ferrite.

If desired, a minor amount of an inorganic oxide additive which promotesdensification or has a particular effect on magnetic properties ofspinel ferrites can be included in the starting powder. Such additivesare well known in the art and include CaO, SiO₂, B₂ O₃, ZrO₂ and TiO₂ .As used herein, the term "ferrite powder" includes any additive whichforms part of the matrix of the present composite. The particular amountof additive is determinable empirically and frequently, it ranges fromabout 0.01 mol % to about 0.05 mol % of the total amount of ferritepowder, i.e. the total amount of matrix-forming powder.

The matrix-forming powder is a sinterable powder. Its particle size canvary. Generally, it has a specific surface area ranging from about 0.2to about 10 meters₂ per gram, and frequently, ranging from about 2 toabout 4 meters² per gram, according to BET surface area measurement.

The organic binding material used in the present process bonds theparticles together and enables formation of the required thin tape ofdesired solids content, i.e. content of matrix-forming powder. Theorganic binding material thermally decomposes at an elevated temperatureranging to below about 600° C., generally from about 100° C. to to about300° C., to gaseous product of decomposition which vaporizes awayleaving no residue, or no significant deleterious residue.

The organic binding material is a thermoplastic material with acomposition which can vary widely and which is well known in the art orcan be determined empirically. Besides an organic polymeric binder itcan include an organic plasticizer therefor to impart flexibility. Theamount of plasticizer can vary widely depending largely on theparticular binder used and the flexibility desired, but typically, itranges up to about 50% by weight of the total organic content.Preferably the organic binding material is soluble in a volatilesolvent.

Representative of useful organic binders are polyvinyl acetates,polyamides, polyvinyl acrylates, polymethacrylates, polyvinyl alcohols,polyvinyl butyrals, and polystyrenes. The useful molecular weight of thebinder is known in the art or can be determined empirically. Ordinarily,the organic binder has an average molecular weight at least sufficientto make it retain its shape at room temperature and generally such anaverage molecular weight ranges from about 20,000 to about 200,000,frequently from about 30,000 to about 100,000.

Representative of useful plasticizers are dioctyl phthalate, dibutylphthalate, diisodecyl glutarate, polyethylene glycol and glyceroltrioleate.

In carrying out the present process, the matrix-forming powder andorganic binding material are admixed to form a uniform or at least asubstantially uniform mixture or suspension which is formed into a tapeof desired thickness and solids content. A number of conventionaltechniques can be used to form the mixture and resulting green tape.Generally, the components are milled in an organic liquid or solvent inwhich the organic material is soluble or at least partially soluble toproduce a castable mixture or suspension. Examples of suitable solventsare methyl ethyl ketone, toluene and alcohol. The mixture or suspensionis then cast into a tape of desired thickness in a conventional manner,usually by doctor blading which is a controlled spreading of the mixtureor suspension on a carrier from which it can be easily released such asTeflon, Mylar or silicone coated Mylar or glass. The cast tape is driedto evaporate the solvent therefrom to produce the present tape which isthen removed from the carrier.

The particular amount of organic binding material used in forming themixture is determinable empirically and depends largely on the amountand distribution of solids desired in the resulting tape. Generally, theorganic binding material ranges from about 25% by volume to about 50% byvolume of the solids content of the tape.

The present tape or sheet can be as long and as wide as desired, andgenerally it is of uniform or substantially uniform thickness. Itsthickness depends largely on its particular application. Generally, thetape has a thickness ranging from about 25 microns to about 1000microns, frequently ranging from about 50 microns to about 900 microns,and more frequently ranging from about 100 microns to about 800 microns.

The metallization-forming material can be any material containing orcomprised of elemental silver or the Ag-Pd alloy which forms the desiredcontinuous metallization of elemental silver or the Ag-Pd alloy in thepresent composite. The metallization-forming material comprised ofelemental silver or Ag-Pd alloy can be in a number of physical formssuch as particulates, or a solid body such as a strip, wire, sheet orpunched sheet.

The metallization-forming material containing elemental silver or theAg-Pd alloy usually is deposited from a suspension, for example, a pasteor ink, of particles of silver or the present Ag-Pd alloy suspended inorganic binder. The suspension is deposited, usually by screen printing,on the face of a tape and, when dry, produces the desired predeterminedpattern of metallization-forming material. Such suspensions are knownand are available commercially, and preferably, they are free of glassfrit. Generally, the metal particles range in size from about 0.1 micronto about 20 microns. Any organic component of the metallization-formingmaterial thermally decomposes at a temperature below about 600° C.leaving no residue or no significant deleterious residue.

A layered structure of at least two of the tapes is formed whichcontains the metallization-forming material therewithin in a desiredpattern. The layered structure can be formed by a number of conventionaltechniques. For example, a pattern of metallization-forming material canbe deposited on the face of a first tape and a second tape can bedeposited on top of the pattern to cover it. Preferably, the tapes aresubstantially coextensive with each other, usually forming asandwich-type structure. The configuration of the layered structureshould permit the formation of the present laminated structure whereinnone of the pattern is exposed to the ambient.

In another embodiment, the metallization-forming material is depositedor printed in a preselected form on the face of a number of tapes.Feedthrough holes may be punched in the tapes as required for layerinterconnection and provided with metallization-forming material toprovide a conductive path. The tapes can then be stacked together,generally one on top of the other, to produce the present layeredstructure wherein the totally deposited metallization-forming materialcomprises a pattern therewithin.

In another embodiment, the present layered structure contains aplurality of separate individual, i.e. discrete, patterns ofmetallization-forming material therewithin.

The layered structure is then laminated under a pressure and temperaturedeterminable empirically depending largely on the particular compositionof the organic binding material to form a laminated structure.Lamination can be carried out in a conventional manner. Laminatingtemperature should be below the temperature at which there isdecomposition, or significant decomposition, of organic binding materialand generally, an elevated temperature below 150° C. is useful and thereis no significant advantage in using higher temperatures. Typically, thelamination temperature ranges from about 35° C. to about 95° C. and thepressure ranges from about 500 psi to about 3000 psi. Generally,lamination time ranges from about 1/2 to about 5 minutes. Also,generally, lamination is carried out in air.

In the laminated structure, none of the pattern is exposed to theambient, i.e. none of the silver is exposed to the ambient.

The metallization-forming material should be present in the laminatedstructure, i.e. the unsintered structure, in an amount at leastsufficient to produce a continuous metallization in the sinteredcomposite. The amount of metallization-forming material can vary withthe particular amount for a given pattern depending largely on thedesired thickness of the metallization in the sintered composite orcomposite product. Such amounts are determinable empirically.

Generally, the laminated structure is plastic, pliable or moldable andit can be arranged or shaped by a number of conventional techniques intoa desired simple, hollow and/or complex form which is retained aftersintering. For example, the laminated structure can be wound around intoa coil in a single plane, or into a spiral form in a plurality ofplanes.

The laminated structure is fired to produce the present composite. At atemperature of less than about 600° C., thermal decomposition of organicmaterial is completed producing a fired porous structure. Thermaldecomposition can be carried out in any atmosphere, generally at aboutor below atmospheric pressure, which has no significant deleteriouseffect on the sample such as, for example, air. If desired, thermaldecomposition may be carried out in a partial vacuum to aid in removalof gases.

The fired structure should have an open volume available to accommodatethe metal, i.e. silver or Ag-Pd alloy, during sintering of the ferritematrix. densifies, i.e. it shrinks in volume, and the silver is totallymolten whereas the Ag-Pd alloy is partially or totally molten. Since themetal is located within the structure, it cannot evaporate to anysignificant extent. Since the metal cannot shrink, it must have an openvolume to squeeze into during sintering. The open accommodating volumeshould be sufficient to prevent bloating of the sintered composite andis determinable empirically. Generally, the open volume which should bemade available to the metal prior to sintering of the ferrite matrixranges from about 30% to about 60% by volume of the total volume ofsilver or Ag-Pd alloy. Preferably, the open volume is about 50% inexcess of the total volume of metal. Also, preferably, no significantamount of the accommodating open volume remains in the sinteredcomposite.

Sufficient open volume can be made available to the metal beforesintering occurs by a number of techniques. It can be produced in thelayered or laminated structures or in the fired structure. The openaccommodating volume is directly connected with the metal prior tosintering but it may be located only at a portion of the pattern, oralong a boundary thereof, or it can be dispersed through the pattern.For example, when the metallization-forming material is totally solid,such as a wire with two end portions, the accommodating volume can becomprised of a depression in the supporting tape open to each endportion.

Preferably, the accommodating volume is produced in the fired structureby depositing the pattern on the tape from a suspension of particles ofelemental silver or of the Ag-Pd alloy, such as by screen printing.Typically, the metal particles occupy only about 50% by volume of thedried screen printed material with the remainder being organic material.The organic material thermally decomposes before sintering occurs andsuch decomposition automatically produces an open volume in the firedstructure of about 50% in excess of the total volume of metal whichfrequently is the required open volume.

The pattern of metallization-forming material in the unsinteredlaminated structure can vary and depends largely on the pattern of themetallization desired in the sintered composite. Generally, the patternis distributed, frequently significantly uniformly, in the unsinteredlaminated structure. In one embodiment, the pattern in the unsinteredlaminated structure has two end portions, and in another embodiment, itis in the form of a circle. However, the pattern in the unsinteredlaminated structure should form a metallization in the sinteredcomposite which permits it to be useful for producing the presentcomposite product.

The fired structure is sintered at a temperature ranging from about1000° C. to about 1400° C., frequently from about 1100° C. to about1300° C., depending largely on its composition and the particularcomposite desired. A temperature below about 1000° C. generally is notoperable to produce the present composite. A temperature higher thanabout 1400° C. provides no advantage and may not produce the presentcomposite.

Sintering is carried out in an oxygen-containing atmosphere thecomposition of which depends largely on the composition of thematrix-forming powder as well as on the matrix composition desired.Also, upon completion of sintering, the sintered product may be cooledin the same atmosphere used for sintering, or in some other atmospheresuch as, for example, an atmosphere which may be needed to maintaincertain matrix compositions. The sintering and cooling atmospheresshould have no significant deleterious effect on the present composite.Generally, the sintering and cooling atmospheres are at aboutatmospheric or ambient pressure, and generally the sintered product iscooled to about room temperature, i.e. from about 20° C. to 30° C. Thesintering and cooling atmospheres for the production of spinel ferritebodies are well known in the art.

As an example, when all of the cations of the matrix-forming powder arein their highest valence, and such valence state is to be retained inthe sintered matrix, sintering is carried out in an oxidizingoxygen-containing atmosphere. In such instance, oxygen generally ispresent in an amount greater than about 50% by volume of the atmosphereand the remaining atmosphere frequently is a gas selected from the groupconsisting of nitrogen, a noble gas such as argon, and a combinationthereof. Usually, the sintering atmosphere is comprised of air oroxygen. Also, in such instance, the sintered product generally is cooledin an oxidizing oxygen-containing atmosphere, usually the sameatmosphere used for sintering, or some other atmosphere in which thesintered product is inert or substantially inert to produce the desiredcomposite.

However, as another example, if the matrix-forming ferrite powdercontains Fe²⁺ cation, or if the Fe³⁺ is to be reduced to produce acertain small amount of Fe²⁺ cation to produce certain magneticproperties, sintering is carried out in a reducing oxygen-containingatmosphere wherein the oxygen content is controlled to produce and/ormaintain the Fe²⁺ cation in the desired amount. Also, in this instance,upon completion of sintering, at least during part of the cooling cycle,the oxygen content of the atmosphere is controlled, usually decreased,to maintain the desired amount of Fe²⁺ cation. Generally, the reducingoxygen-containing atmosphere is comprised of oxygen and nitrogen or aninert gas such as argon wherein the effective amount of oxygen generallyranges up to about 10% by volume of the atmosphere.

Generally, sintering can be controlled in a conventional manner, i.e. byshortening sintering time and/or lowering sintering temperature, toproduce a sintered matrix having a desired density or porosity or havinga desired grain size. Sintering time may vary widely and generallyranges from about 5 minutes to about 5 hours. Usually, the longer thesintering time or the higher the sintering temperature, the more denseis the matrix and the larger is the grain size.

In one embodiment of the present invention, where silver or Ag-Pd wirehaving a diameter of less than about 5 mils is used to form themetallization, or part of the metallization, in the sintered composite,open volume generally need not be provided to accommodate the moltenmetal during sintering. In such instance, plastic deformation of thematrix during sintering may accommodate ferrite shrinkage withoutcracking the sample. In this embodiment, the wire can vary in length asdesired but generally its length is greater than about 10 mils.

The present sintered matrix has a porosity ranging from about 0%, orabout theoretical density, to about 40% by volume of the sinteredmatrix. The particular porosity depends largely on the particularmagnetic properties desired. For several applications, the porosity ofthe sintered matrix ranges from about 5% to about 30%, or from about 10%to about 25%, and frequently it is about 15%, by volume of the totalvolume of the matrix. Generally, the lower the porosity of the matrix,the higher is its magnetic permeability. In the present composite,porosity is distributed therein, preferably significantly orsubstantially uniformly. Generally, the pores in the sintered matrixrange in size from about 1 micron to about 100 microns, frequently fromabout 10 microns to about 70 microns. The pores may be closed and/orinterconnecting.

Generally, the average grain size of the present sintered matrix rangesfrom about 5 microns to about 100 microns, frequently from about 10microns to about 80 microns, or from about 20 microns to about 60microns, or from about 30 microns to about 50 microns. Generally, withincreasing grain size, the magnetic permeability of the compositeincreases. On the other hand, generally with decreasing grain size, thelower are the electrical losses.

The present sintered composite is comprised of a polycrystalline matrixof ferrite totally enveloping a continuous metallization of elementalsilver or of a Ag-Pd alloy ranging to 25 atomic % Pd. The sinteredferrite matrix is in direct contact with the metallization. In oneembodiment, the present composite contains a plurality of continuousmetallizations of silver alone, or of the Ag-Pd alloy, which areelectrically isolated from each other. Frequently, each metallizationhas two end portions. The presence of the metallization in the compositecan be determined by x-ray.

The present invention enables the direct production of a sinteredcomposite of desired shape and size. The sintered composite is free ofbloating.

The present sintered composite is useful for producing a compositeproduct which is comprised of the ferrite matrix enveloping acontinuous, i.e. electrically conductive, metallization of silver or thepresent Ag-Pd alloy with two end portions, wherein only both endportions are exposed to the ambient and are at least sufficient forelectrical contact to be made such as, for example, by soldering a leadthereon.

A number of conventional techniques can be used to produce the compositeproduct. In one embodiment, where the sintered composite contains ametallization with two end portions, a portion of the matrix can beremoved, for example by polishing it off, to expose the end portions. Inanother embodiment, the sintered composite is sliced or cut, for exampleby means of a diamond saw, to produce one or more of the presentcomposite products. In yet another embodiment, where the sinteredcomposite contains a plurality of electrically isolated continuousmetallizations, it can be sliced to produce one or more compositeproducts with a plurality of electrically isolated continuousmetallizations wherein each metallization has two end portions which areexposed to the ambient.

The continuity of the metallization in the composite product can bedetermined by a number of conventional techniques such as, for example,by contacting its exposed end portions with leads to determineelectrical conductivity.

The thickness of the electrically conductive metallization in thesintered composite or composite product can vary depending largely onits application. Generally, it ranges from about 2 to about 800 microns,frequently from about 20 to about 150 microns.

The present sintered ferrite matrix is a soft magnetic material of cubicsymmetry. Its composition is the same as that given herein for thematrix-forming material. It can be magnetized but loses itsmagnetization when the source of magnetization is removed. For example,when a voltage is applied across both exposed end portions of themetallization in the present composite product, current is passedtherethrough producing a magnetic field which magnetizes the ferritematrix thereby storing electrical energy therein. When the voltage isremoved, the ferrite matrix will demagnetize giving back the electricalenergy as a reverse electrical current in the metallization.

The present composite product has a number of uses. It is useful as anelectrical component in an electrical circuit. It is particularly usefulas an electrical inductor such as, for example, a tuning coil or afilter coil.

When the present composite product contains two or more separatemetallizations, i.e. conductors or windings, each of which is accessedby two exposed end portions, such a composite product is useful as anelectrical transformer.

The invention is further illustrated by the following examples whereinthe procedure was as follows unless otherwise stated:

An air furnace with molybdenum disilicide heaters was used.

The firing, sintering and cooling was carried out in air at aboutatmospheric pressure.

The ferrite powder was a sinterable powder.

The organic binding material used to form the tape was comprised ofcommercially available organic binder comprised of polyvinylbutyral(average molecular weight of about 32,000) and commercially availableliquid plasticizer comprised of polyunsaturated hydroxylatedlow-molecular weight organic polymers. Specifically, the organic bindingmaterial was comprised of 4.13 grams of polyvinylbutyral and 1.48 gramsof liquid plasticizer per 100 grams of ferrite powder.

The screen printing ink was a commercially available ink comprised of asuspension of silver particles in a solution of organic binder. About50% by volume of the dried screen printed material was comprised ofsilver particles with the remainder being organic material.

In the laminated structure, none of the silver was exposed to theambient.

Standard techniques were used to characterize the composite for density,microstructure and electrical properties.

EXAMPLE 1

A calcined ferrite powder having a composition comprised of 14.12 mol %NiO, 24.45 mol % ZnO, 1.15 mol % MnO and 60.28 mol % Fe₂ O₃ was used. Ithad a specific surface area of about 1 m^(2/) g.

Ferrite tapes were prepared by the tape casting technique. 5.61 grams ofthe organic binding material were dissolved at ambient temperature in 50grams of a mixture of 33 grams of toluene and 17 grams of methylalcohol. The resulting solution was admixed with 100 grams of ferritepowder in a ball mill for about 4 hours at room temperature. Theresulting slurry was tape cast on a Mylar sheet using a doctor blade,then dried in air at room temperature and atmospheric pressure to removethe solvent, and the resulting tape was stripped from the Mylar sheet.

Each tape was about 6 inches wide, 30 inches long and had asubstantially uniform thickness of about 20 mils. Ferrite powder wasdistributed in each tape substantially uniformly and comprised about 52%by volume of the tape.

Each tape was cut to lengths of about 1.5 inches and width of about 1.5inch to form blanks.

With a screen mask, a pattern was screen printed on a face of a singlelayer blank to form a pattern which was a partially closed circle withtwo extending, parallel legs (a Greek letter Omega shape). The outsidediameter of the partial circle was 0.900 in., the trace width wasuniformly 0.100 in., the legs extended from the circle perimeter byabout 0.25 in. The screen printing was dried in air at room temperatureand when dried was about 1 mil thick.

An unprinted blank was placed on top of the printed blank covering thepattern and forming essentially a sandwich structure. This structure waslaminated in air in a laminating press at about 93° C. under a pressureof about 800 psi for about 1/2 minute. No portion of the patternextended to any surface of the resulting laminated structure.

The laminated structure was placed in an open alumina boat and fired inair. As the temperature was raised, the organic component thermallydecomposed and vaporized away below 600° C. The sample was sintered at atemperature of about 1280° C. for 30 minutes and then furnace-cooled toroom temperature.

The resulting composite was comprised of a polycrystalline ferritematrix which totally enveloped a phase of elemental silver.

From other work it was known that the ferrite matrix had a compositionwhich was the same as, or did not differ significantly from, that of thestarting ferrite powder, and that it was of cubic symmetry.

A rotating diamond saw was used to cut off a portion of the ferritematrix which was then polished in a standard manner to expose the twoleg portions of the silver phase thereby producing the present compositeproduct. Electrical resistance measurements between the leg sections wasless than 0.1 ohm. Since the resistivity of the ferrite matrix wasgreater than 1 megohm-cm, the electrical measurements of the silverphase, i.e. trace, showed that the silver conduction path wascontinuous. A structure of this type would be useful as an electricalinductor.

For examination purposes, a portion of the matrix was cut and polishedaway across the circle portion of the omega-shaped silver phase.Examination of the resultant product, as well as an x-ray of thesintered composite before it was cut, showed that the silvermetallization was fully retained within the sintered matrix anduniformly shrank in trace width and shape to accommodate about a 19%linear shrinkage of both the silver ink deposit and the ferrite. Thesintered ferrite matrix showed a grain size of about 10 microns and aporosity of about 10 volume %. The final silver trace was almost it'sinitial thickness (about 1 mil).

EXAMPLE 2

Two printed blanks and an unprinted blank were produced as disclosed inExample 1. The blanks were assembled into a three layer structure withthe blanks substantially coextensive with each other and the two printedpatterns separated and within the structure. The layered structure waslaminated as disclosed in Example 1.

In the laminated structure, none of the patterns were exposed to theambient.

The laminated structure was fired in the same manner as disclosed inExample 1 and furnace-cooled to room temperature.

The resulting composite was comprised of a polycrystalline ferritematrix which totally enveloped each of two electrically isolatedcontinuous phases of elemental silver. The sintered composite showed byx-ray two separate, continuous silver phases.

The sintered composite showed a linear shrinkage of about 19%.

Standard structural analysis of the sintered composite showed that thesilver phase, i.e. windings, were continuous and electrically isolatedfrom one another, each with a thickness of about 1 mil. The ferritematrix showed the same structural characteristics as the matrix producedin Example 1.

A structure of this kind, i.e. the sintered composite product whichcould be produced by removing portions of the matrix to expose the twoend portions of each silver phase, would be useful as an electricaltransformer.

EXAMPLE 3

Several unprinted ferrite tapes, i.e. blanks, were produced as disclosedin Example 1.

A sandwich structure of three blank layers, i.e. the layers werecoextensive with each other, was laminated as disclosed in Example 1.Several of such three layer laminated structures were produced.

Solid strips of elemental silver about 5/8inch long and 0.125 inch by0.003 inch cross-section were used.

A silver strip was placed on top of the three layer laminated structure,i.e. on a face thereof, and two additional ferrite blank layers wereplaced on top of the silver to form a five layer sandwich structurewhich was laminated as disclosed in Example 1. None of the silver in thelaminated structure was exposed to the ambient. Three such five layerlaminated structures were produced and are shown as Runs 1-in Table I.

A slot was machined into a face of the remaining three layer laminatedstructures. A silver strip was placed in each slot. Each slot was 0.003inch deep by 5/8inch long. The slots varied in width to accommodateexcess volumes in the slots unoccupied by the silver strips in amountsequal to 15, 20, 25, 30, 50 and 60% of the initial volume of theindividual solid silver strip. Two additional blank layers were placedon top of each silver strip to form a five layer sandwich structurewhich was laminated as disclosed in Example 1. None of the silver in thelaminated structures was exposed to the ambient.

Each of the laminated structures was fired in the same manner asdisclosed in Example 1 and furnace-cooled to room temperature. Theresults are shown in Table I.

                                      TABLE I    __________________________________________________________________________              Excess    Silver                              Silver                                    Sintered       Sample Slot                  Shrinkage                        Conductor                              Conductor                                    composite    Run       No.    Vol. %                  % linear                        thickness                              form  integrity    __________________________________________________________________________    1  Q1MT    8A         0  19    3 mil discont.                                    catastroph-    8B  0  19 "   "     ically    3    8C  0  19 "   "     cracked    4  Q1MT    9A 15  18 "   continuous                        small    5    9B 20  "  "   "     internal    6    9C 25  "  "   "     cracks    7    9D 30  "  "   "     sound    8  Q1MT    13A       50  19 "   continuous                        sound    9    13B       60  "  "   "     "    __________________________________________________________________________

Runs 7-9 illustrate the present invention. In the sintered composites ofRuns 7-9, none of the silver phase was exposed to the ambient and theferrite matrices showed a grain size, shrinkage and porosity which weresubstantially the same as that disclosed for the ferrite matrix inExample 1. The sintered composites of Runs 7-9 were free of bloating.

The results in Table I show that by incorporating an appropriate excessinternal volume around the metallization which is sufficient to accountfor the volume shrinkage of the ferrite during co-firing, integralstructures of ferrite with continuous pure silver conductors may beobtained without providing access of the metallizations to a freesurface for liquid metal pressure equalization and without developinginternal pressures which crack the body. Table I shows that such excessvolume ranges from about 30% to about 60% of the elemental silver withinthe unsintered structure.

If portions of the ferrite matrix were removed from the sinteredcomposites produced in Runs 7-9 to expose only both end portions of eachsilver phase, the resulting composite products would be useful aselectrical inductors.

EXAMPLE 4

Several unprinted ferrite tapes, i.e. blanks, were produced as disclosedin Example 1.

A sandwich structure of three blank layers, i.e. the layers werecoextensive with each other, was laminated as disclosed in Example 1.

Solid wires of elemental silver half-inch long and 25 mil in diameterwere used.

A pocket was machined into a face of the laminated structure. A silverwire was placed across the pocket. Two additional blank layers wereplaced on top of the silver wire to form a five layer sandwich structurewhich was laminated as disclosed in Example 1. None of the silver in thelaminated structure was exposed to the ambient. The pocket wasgeometrically centered within the resulting laminated structure and wasmachined to accept the wire with a pocket volume of about 50% in excessof the wire volume.

A second five layer laminated structure was prepared in the same mannerexcept that the pocket was machined to accept the wire with a pocketvolume of about 60% in excess of the wire volume.

The five layer laminated structures were fired at about 1280° C. for 30minutes in an open boat in air and then cooled to room temperature.

In the resulting sintered composites, none of the silver was exposed tothe ambient.

The resulting sintered composites were free of cracks and warpage andshowed by x-ray that the wires remained continuous and also assumed thegeneral shape of the original machined pockets reduced by a linearshrinkage of about 20%. The wire embedded in the pocket of 50% excessvolume showed a smoother conformation to the original pocket shapeindicating that the preferred excess volume for the silver toaccommodate ferrite shrinkage is about 50%.

If portions of the ferrite matrix were removed from the sinteredcomposites to expose only both end portions of each silver phase, theresulting composite products would be useful as electrical inductors.

What is claimed is:
 1. A composite comprised of a polycrystallineferrite matrix totally enveloping a continuous metallization comprisedof elemental silver or Ag-Pd alloy ranging from an amount detectable bymicroprobe analysis to 25 atomic % Pd, said ferrite matrix having anelectrical resistivity greater than 500 ohm-centimeters at a temperatureranging from about 20° C. to about 100° C., said ferrite matrix rangingup to about 40% by volume in porosity, said composite being useful forproducing a composite product containing a continuous metallization withtwo end portions wherein only said end portions of said metallizationare exposed at least sufficiently for electrical contact to be madetherewith.
 2. The composite according to claim 1 wherein saidmetallization is distributed in said composite in substantially a singleplane.
 3. The composite according to claim 1 wherein said metallizationis distributed in said matrix in a plurality of planes.
 4. The compositeaccording to claim 1 in the form of a coil in substantially a singleplane.
 5. The composite according to claim 1 in the form of a spiral ina series of planes.
 6. The composite according to claim 1 which containsa plurality of said metallizations, said metallizations beingelectrically isolated from each other, said composite being useful forproducing a composite product containing a plurality of continuousmetallizations wherein each metallization has two end portions andwherein only said end portions of said metallizations are exposed atleast sufficiently for electrical contact to be made therewith.
 7. Thecomposite according to claim 1 wherein said ferrite matrix has acomposition comprised of MO(Fe₂ O₃)₁±x where x has a value ranging from0 to about 0.2 and where M is a divalent metal cation selected from thegroup consisting of Mg, Mn, Fe, Co, Ni, Zn, Cu and combinations thereof.8. A composite product comprised of a polycrystalline ferrite matrixcontaining an electrically conductive continuous metallization comprisedof an alloy of silver and palladium ranging from an amount detectable bymicroprobe analysis to 25 atomic % of palladium, said metallizationhaving two end portions and having only said end portions exposed atleast sufficiently for electrical contact to be made therewith, saidferrite matrix having an electrical resistivity greater than 500ohm-centimeters at a temperature ranging from about 20° C. to about 100°C., said ferrite matrix ranging up to about 40% by volume in porosity.9. The composite product according to claim 8 wherein said metallizationis distributed in said product in substantially a single plane.
 10. Thecomposite product according to claim 8 wherein said metallization isdistributed in said matrix in a plurality of planes.
 11. The compositeproduct of claim 8 in simple, hollow and/or complex form.
 12. Thecomposite product according to claim 8 in the form of a coil insubstantially a single plane.
 13. The composite product according toclaim 24 in the form of a spiral in a series of planes.
 14. Thecomposite product according to claim 8 which contains a plurality of themetallizations, said metallizations being electrically isolated fromeach other.
 15. The composite product according to claim 8 wherein saidferrite matrix has a composition comprised of MO(Fe₂ O₃)₁±x where x hasa value ranging from 0 to about 0.2 and where M is a divalent metalcation selected from the group consisting of Mg, Mn, Fe, Co, Ni, Zn, Cuand combinations thereof.
 16. The composite according to claim 8 whereinsaid ferrite matrix is a nickel zinc manganese ferrite.
 17. A compositeproduct comprised of a polycrystalline ferrite matrix containing anelectrically conductive continuous metallization comprised of an alloyof silver and palladium ranging from an amount detectable by microprobeanalysis to 25 atomic % of palladium, said metallization having two endportions and having only said end portions exposed, said ferrite matrixhaving an electrical resistivity greater than 500 ohm-centimeters at atemperature ranging from about 20° C. to about 100° C., said ferritematrix having a porosity ranging from about 5% to about 30% by volume,said porosity being distributed in said matrix.
 18. The compositeproduct according to claim 17, wherein said metallization is distributedin said product in substantially a single plane.
 19. The compositeproduct according to claim 17, wherein said metallization is distributedin said matrix in a plurality of planes.
 20. The composite product ofclaim 17, wherein said porosity ranges from about 10% to about 25%. 21.The composite product according to claim 17, wherein said porosity isabout 15%.
 22. The composite product according to claim 17, whichcontains a plurality of the metallizations, said metallizations beingelectrically isolated from each other.
 23. The composite productaccording to claim 17, wherein said ferrite matrix has a compositioncomprised of MO(Fe₂ O₃)₁±x where x has a value ranging from 0 to about0.2 and where M is a divalent metal cation selected from the groupconsisting of Mg, Mn, Fe, Co, Ni, Zn, Cu, and combinations thereof. 24.The composite product according to claim 17, wherein said ferrite matrixis a nickel zinc manganese ferrite.
 25. A composite product comprised ofa polycrystalline ferrite matrix containing an electrically conductivecontinuous metallization comprised of an alloy of silver and palladiumranging from 1 atomic % to 20 atomic % of palladium, said metallizationhaving two end portions and having only said end portions exposed, saidferrite matrix having an electrical resistivity greater than 500ohm-centimeters at a temperature ranging from about 20° C. to about 100°C., said ferrite matrix having a porosity ranging from about 5% to about30% by volume, said porosity being distributed in said matrix.
 26. Thecomposite product according to claim 25, wherein said palladium rangesfrom 2 atomic % to 10 atomic %.